The World Health Organization (WHO) is a specialized agency of the United Nations that is concerned with international public health. A user at the primary level may not be trained to assess hearing loss nor how audiological equipment should be calibrated and maintained.
WHO defines disabling hearing impairment in adults as a permanent unaided hearing threshold level (average for frequencies 0.5, 1, 2, 4 kHz) for the better ear of 41 dB or greater. WHO classifies hearing impairment into 5 grades ranging from no or slight hearing problems to unable to hear and understand even a shouted voice. The 5 grades encompass distinct ranges of hearing loss and each grade has an associated hearing aid indication (recommendation). WHO suggests that hearing aids may be needed for those with slight hearing impairment, and more strongly recommends hearing aids for higher levels of impairment. WHO grades of 2, 3, and 4 are classified as disabling hearing impairment.
WHO hearing impairment grading is determined according to the hearing threshold, which is the lowest intensity at which sound is just audible to a person. The hearing testing method required for determining WHO hearing impairment grading is essentially an audiogram test. The instrumentation and accessories for standard audiometric evaluation are generally specialized electro-medical devices for use in a clinical setting. For example, to obtain a valid audiogram report, tests are generally performed in specialized sound-isolated rooms, often referred to as a “sound booth,” to reduce noise levels present in the environment in order to test hearing ability down to 0 or −10 dB HL (see, e.g., ANSI S3.1: American Standard Maximum Permissible Ambient Noise Levels for Audiometric Rooms). The combined cost of a sound booth and clinical instrumentation for standard audiogram testing can easily exceed $20,000.
Performing a hearing assessment is generally not practical for lay people to self-administer or administer to others, particularly in home, office, or retail store settings. Even in quiet room environments, noise levels typically exceed the maximum level allowed for determining the threshold of hearing. Another limitation for hearing test administration outside clinical settings is the complexity associated with the test procedure, which can be perplexing and time consuming for a lay person. Further, conducting a test and hearing threshold search in 5 dB increments, as defined by standard audiometric methods is relatively time-consuming and results do not convey a hearing aid indication to a consumer.
Current hearing evaluation methods and associated reports are generally designed for administration and interpretation by hearing professionals, such as an audiologist, an otolaryngologist, a hearing aid dispenser, etc. Audiogram results are generally of little value to a lay consumer and generally present irrelevant information pertaining to hearing aid candidacy. The audiogram test report, generally considered the standard form for hearing assessment and hearing aid prescription, is technical and not suitable for interpretation by a potential hearing aid consumer. For example, an audiogram report generally presents a person's hearing sensitivity for tonal sounds from −10 to 110 dB, inversely displayed, versus test frequencies from 125 to 8000 Hz. Although hearing sensitivity for each frequency may also be tabulated in other audiogram forms, they are generally not useful for a lay consumer, particularly for indicating hearing aid candidacy. Furthermore, determining the hearing ability in certain level ranges, such as −10 to +15 dB HL, is generally not relevant to a person's ability to carry on normal conversations. Another barrier for performed hearing assessment by a non-expert is related to the aforementioned cost, complexity and inaccessibility of standard hearing test instruments.
To circumvent some of the limitations of standard hearing evaluation methods, automated, computer-based hearing evaluation methods have been proposed, including self-administered online tests using personal computers and smartphones. These tests are often inadequate due to their inaccuracy caused by audio characteristics of consumer electronics not meeting the standards of audiometric testing. In addition to the aforementioned obstacles related to audio characteristics, the calibration of acoustic signals emanating from a consumer transducer (a consumer earphone or a speaker, for example) represents a daunting challenge, preventing accurate hearing evaluation by the lay consumer using a personal computer, or a personal electronic device.
Hearing screening tests offer basic hearing assessment for individuals on the basis of a pass or fail criteria. Generally speaking, these tests are administered by a hearing professional or a nurse, using a portable instrument, which produces a limited set of test stimuli often at a predetermined level between 20 and 40 dB HL depending on the age of the group being tested. A major drawback of current hearing screening methods is the lack of sensitivity and specificity for determining the hearing ability and indicating hearing aid candidacy. As a result, “failed” subjects are generally referred to a hearing professional for further hearing assessment prior to hearing aid candidacy assessment and hearing aid fitting.